Apparatus for forming hydrogen

ABSTRACT

A hydrogen producing apparatus comprising: a reforming section having a reforming catalyst which causes a reaction between a carbon-containing organic compound as a feedstock and water; a feedstock supply section for supplying the feedstock to the reforming section; a water supply section for supplying water to the reforming section; a heating section for heating the reforming catalyst; a shifting section having a shift catalyst which causes a shift reaction between carbon monoxide and water contained in a reformed gas supplied from the reforming section; and a purifying section having a purifying catalyst which causes oxidation or methanation of carbon monoxide contained in a gas supplied from the shifting section, wherein the shift catalyst comprises a platinum group metal and a metal oxide.

TECHNICAL FIELD

The present invention relates to a hydrogen producing apparatus forsupplying hydrogen to fuel cells or the like.

BACKGROUND ART

Cogeneration systems using a fuel cell having high power-generationefficiency are receiving special attention as decentralized powergeneration systems capable of effective utilization of energy. Many ofthe fuel cells, for example, phosphoric acid fuel cells currentlycommercially available and polymer electrolyte fuel cells currentlyunder development, use hydrogen as a feedstock to generate electricpower. Fuel infrastructure for hydrogen, however, has not yet been builtup and the hydrogen therefore needs to be produced on a site where thecell is installed. Methods for producing the hydrogen includes a steamreforming method and an auto-thermal method. In the methods, acarbon-containing organic compound as the feedstock, for example,natural gas, hydrocarbon such as LPG, alcohol such as methanol, naphthaor the like is reacted with water in a reforming section having areforming catalyst, to produce the hydrogen.

In the steam reforming reaction, carbon monoxide (CO) is generated as aby-product. Since the CO becomes a poisoning component of the electrodecatalyst of the fuel cell especially in polymer electrolyte fuel cellsthat operate at low temperatures, there are also provided a shiftingsection in which a shift reaction converts water and the CO to hydrogenand carbon dioxide and a purifying section in which the CO is subjectedto an oxidation or methanation reaction. In the shifting section, it iscommon to use a Fe—Cr based catalyst at temperatures from 300 to 500° C.or a Cu—Zn based catalyst at temperatures from 200 to 300° C. Since theFe—Cr based catalyst is used at high temperatures, large reduction of COis not possible. Since the Cu—Zn based catalyst is used at relativelylow temperatures, the CO can be decreased to a considerably lowconcentration. Thus, the Cu—Zn based catalyst is used in the shiftingsection to eventually decrease the CO down to a concentration of about0.5%. Also, in the purifying section, platinum group metal Pt or Rubased catalyst is used to selectively oxidize or methanize the CO, sothat the CO is ultimately decreased down to a level of about 20 ppm.

The Cu—Zn based catalyst is active for the shift reaction while it is ina reduced state. When the apparatus is operated continuously, the Cu—Znbased catalyst is constantly in a reduced state, and therefore theactivity of this catalyst hardly deteriorates. However, in the case ofintermittent operations in which the apparatus is started and stoppedrepeatedly or in other cases, air gets into the shifting section tooxidize the catalyst, so that the activity of the catalyst deterioratessignificantly. Further, the problem of catalyst activity deteriorationarises also when the catalyst is used at high temperatures not lowerthan 300° C. and in other cases.

In order to improve acid resistance and thermal resistance, there is aproposal to use a catalyst of platinum group metal supported on a metaloxide as the shift catalyst. This catalyst of platinum group metalsupported on a metal oxide hardly aggregates due to sintering of thecatalyst even when used at a temperature of about 500° C. It also has anexcellent feature that the catalyst activity does not change even in anoxidized state. However, in comparison with the Cu—Zn based catalyst,the reactivity at low temperatures may deteriorate slightly. Thisdeterioration increases the CO concentration at the outlet of theshifting section and produces a problem that the conventional Pt or Rubased catalyst of the purifying section is unable to decrease the COsufficiently.

Also, the above-described catalysts have a different reactiontemperature and the catalysts therefore need to be heated up to thereaction temperature in order to facilitate stable supply of thehydrogen. The temperature is controlled to about 700° C. in thereforming section and about 500 to 200° C. in the shifting section.Since the temperature of the reforming section, which is locatedupstream of the feedstock flow, is high, heat from the reformingsection, for example, heat contained in the reformed gas or excessiveheat of a heating section of the reforming section, is often utilized toheat the shifting section in the hydrogen producing apparatus accordingto the steam reforming method.

In the conventional heating method in which the heat of the reformed gasreleased from the reforming section is utilized to heat the shiftingsection, it takes a long time for the catalyst temperature to becomestable in correspondence with the thermal capacity of each reactionsection. A hindrance to this temperature stabilization is condensationof water in the gas which takes place at low temperature parts of thegas flow route during the heating operation.

On the other hand, when a hydrocarbon based fuel is steam reformed,water is supplied in an amount greater than the necessary amount ofwater for reforming the hydrocarbon in order to prevent deposition ofcarbon. For example, when the feedstock is a hydrocarbon such as methaneor LPG, it is a common practice to supply water which is equal to ormore than 2.5 times the number of carbon atoms to facilitate steamreforming. This causes the gas released from the reforming section tocontain a considerable amount of steam.

However, since the temperature does not rise to the boiling point orhigher where condensation of water takes place, the water needs to bere-evaporated promptly in order to raise the temperature of eachreaction section.

Also, when the apparatus is started from room temperature, in theshifting section and other parts that are heated by the heat containedin the reformed gas, condensation of excessive steam in the reformed gastakes place.

This condensation of water gives rise to following problems.

The first problem is that the temperature will not rise at a part wherecondensation has took place until condensed water evaporates again. Forstable production of the hydrogen, the temperature of each section needsto be raised to a predetermined temperature promptly. However, heat isexchanged promptly between the gaseous steam and, for example, the wallsof the apparatus, to cause condensation of water, but heat exchangebetween the liquid and, for example, the walls of the apparatus becomesa rate-determining step in evaporating the condensed water, therebymaking the evaporation speed slow. The shifting section, in particular,has the shift catalyst having a large thermal capacity and a largeamount of water therefore condenses. As a result, it takes a longer timeto heat the shift catalyst up to an optimal reaction temperature, makingthe start-up time longer. Thus, reduction of the start-up time becomes alarge problem with respect to apparatus operation in the apparatus to besubjected to frequent starts and stops.

The second is that the condensed water causes the catalytic activity ofthe shift catalyst to deteriorate. The Cu—Zn based catalyst having highcatalytic activity is widely used as the shift catalyst. This catalystis highly active while being in a reduced state. Since the catalyst isused at temperatures from 200 to 300° C., condensation of water does notoccur and the catalyst can be maintained in a reduced state during thenormal operation. When condensation of water takes place, however, thecatalyst is oxidized by the water, so that the catalytic activitydeteriorates remarkably. Thus, frequent starts and stops will cause thecatalytic activity to deteriorate significantly, resulting in anincrease in the CO concentration of the shifted gas. Particularly in anapplication as a hydrogen producing apparatus for supplying hydrogen toa solid polymer electrolyte fuel cell, the increase of CO impairs thepower generating characteristics significantly, presenting a seriousproblem.

Many of the phosphoric acid fuel cells, which have already becomecommercially available, are operated continuously with fewer start-upoperations, and the respective reaction sections are not heatedfrequently. On the other hand, fuel cells having a small powergenerating capacity, intended for home use or the like, are assumed tobe subjected to frequent starts and stops of the apparatus. Thus, inorder to reduce the start-up time of such apparatus with frequent startsand stops, it becomes a requisite to reduce condensation of water asmuch as possible.

Also, when condensation of water takes place over the shift catalyst,the catalyst is oxidized and the shift reaction of water and CO isthereby impeded. This is one of the causes of the deterioration of theproperties of the shift catalyst in the hydrogen producing apparatuswith a large number of starts and stops of the apparatus. Especially inthe Cu—Zn catalyst, which is highly active while in a reduced state, thereactivity is markedly deteriorated by the oxidation of the catalyst bywater.

As described above, maintaining the catalytic activity also requiresmaximum reduction of water condensation.

The present invention solves the above-described problem with respect tothe shifting section in the above-described conventional hydrogenproducing apparatus, effectively decreases carbon monoxide in a hydrogengas generated by fuel reforming, and aims to provide a hydrogenproducing apparatus capable of supplying the hydrogen gas in a stablemanner with a simple constitution.

Also, the present invention facilitates an activation process of the COshift catalyst, eliminates the influence of oxygen inclusion when thestart and stop operations are repeated, and aims to provide a hydrogenproducing apparatus which can operate in a stable manner over a longperiod.

Further, the present invention suppresses water condensation in theshifting section upon the start of the hydrogen producing apparatus,thereby to reduce the start-up time of the apparatus, prevent activitydeterioration of the shift catalyst, and realize stable supply ofhydrogen.

DISCLOSURE OF INVENTION

The present invention provides a hydrogen producing apparatuscomprising: a reforming section having a reforming catalyst which causesa reaction between a carbon-containing organic compound as a feedstockand water; a feedstock supply section for supplying the feedstock to thereforming section; a water supply section for supplying water to thereforming section; a heating section for heating the reforming catalyst;a shifting section having a shift catalyst which causes a shift reactionbetween carbon monoxide and water contained in a reformed gas suppliedfrom the reforming section; and a purifying section having a purifyingcatalyst which causes oxidation or methanation of carbon monoxidecontained in a gas supplied from the shifting section, wherein the shiftcatalyst comprises a platinum group metal and a metal oxide.

The metal oxide of the shift catalyst preferably comprises at least oneof cerium oxides and zirconium oxides.

In a preferred embodiment of the present invention, the apparatusfurther comprises an oxygen gas supply section for supplying an oxygengas to the shifted gas, and the catalyst of the purifying sectioncomprises at least Pt and Ru.

The purifying catalyst preferably comprises a Pt—Ru alloy.

In another preferred embodiment of the present invention, the shiftingsection has a heating section for heating the shift catalyst, and theheating section is controlled such that the shift catalyst is heated toa temperature not lower than the dew point of the gas supplied from thereforming section to the shifting section.

In sill another preferred embodiment of the present invention, theapparatus further comprises an air supply section for supplying air tothe gas supplied from the reforming section to the shifting section, andthe amount of air supplied from the air supply section is controlledsuch that the temperature of the shift catalyst becomes not lower thanthe dew point of the gas.

In a preferred embodiment of the present invention, the apparatusfurther comprises a temperature detector for detecting the temperatureof the catalyst of the shifting section and dew point controlling meansfor controlling the dew point of the gas supplied from the reformingsection to the shifting section, wherein the reformed gas, of which dewpoint is lowered by the dew point controlling means, is supplied to theshifting section.

The dew point controlling means is an air supply section for supplyingair to the reforming section together with the feedstock and water, andthe dew point of the gas released from the reforming section is loweredby the air supplied from the air supply section to the reformingsection.

In another preferred embodiment of the present invention, the shiftingsection is divided into plural catalytic reaction chambers each havingthe shifting catalyst, and at least one of a heat radiating part and acooling part is provided between the catalytic reaction chambers.

In a first catalytic reaction chamber in the flowing direction of thereformed gas, the catalyst temperature is preferably retained at notlower than 300° C. and not higher than 450° C.

Of the plural catalytic reaction chambers, the catalyst temperature ispreferably lower in a downstream chamber than in an upstream chamber inthe flowing direction of the reformed gas.

Of the plural catalytic reaction chambers, the catalyst volume ispreferably greater in a downstream chamber than in an upstream chamberin the flowing direction of the reformed gas.

Of the plural catalytic reaction chambers, the amount of the platinumgroup metal supported on the catalyst is preferably greater in adownstream chamber than in an upstream chamber in the flowing directionof the reformed gas.

Of the catalytic reaction chambers, the catalyst of at least one chamberof a second chamber and subsequent chambers preferably contains copperas a component.

A catalytic reaction chamber having a catalyst containing the platinumgroup metal is preferably provided downstream of the catalytic reactionchamber having the catalyst containing copper as a component.

A diffusing part or a mixing part of the reformed gas is preferablyprovided between the catalytic reaction chambers.

The apparatus preferably comprises a controlling section for controllingthe operation of the cooling part on the basis of the temperature of theshift catalyst.

Heat collected by the cooling part is preferably used to heat at leastone of the feedstock and water to be introduced to the reforming sectionand the reformed gas to be introduced to the shifting section.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view schematically showing theconstitution of a hydrogen producing apparatus in a first embodiment ofthe present invention.

FIG. 2 is a longitudinal cross-sectional view schematically showing theconstitution of a hydrogen producing apparatus in a second embodiment ofthe present invention.

FIG. 3 is a longitudinal cross-sectional view schematically showing theconstitution of a hydrogen producing apparatus in a third embodiment ofthe present invention.

FIG. 4 is a longitudinal cross-sectional view schematically showing theconstitution of a hydrogen producing apparatus in a fourth embodiment ofthe present invention.

FIG. 5 is a longitudinal cross-sectional view schematically showing theconstitution of a shifting section of a hydrogen producing apparatus ina fifth embodiment of the present invention.

FIG. 6 is a graph showing the typical relationship between the operatingtemperature of a shift catalyst and the carbon monoxide concentrationafter passage of the catalyst.

FIG. 7 is a longitudinal cross-sectional view schematically showing theconstitution of a shifting section of a hydrogen producing apparatus ina sixth embodiment of the present invention.

FIG. 8 is a longitudinal cross-sectional view schematically showing theconstitution of a shifting section of a hydrogen producing apparatus ina seventh embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, embodiments of the present invention will be describedin detail with reference to drawings.

Embodiment 1

FIG. 1 is a schematic view showing the constitution of a hydrogenproducing apparatus in one embodiment of the present invention.

Numeral 10 represents a reforming section having a reforming chamber 11in which a reforming catalyst is accommodated and a heating section 12for heating the reforming chamber 11. The reforming catalyst is aplatinum group metal supported on a pelletized catalyst carrier composedof alumina, for example, one marketed under the trade name of E catalystby N. E. CHEMCAT Corporation. The heating section 12 is a flame burnerwhich heats the catalyst of the reforming chamber to a temperature of700 to 750° C. The heating section may be any heating means capable ofheating to the intended temperature and is not limited to the flameburner. To the reforming chamber 11 of the reforming section 10, afeedstock composed mainly of hydrocarbon for steam reforming reaction issupplied from a feedstock supply section 13 through a feedstock supplyconduit 14 and water is supplied from a water supply section 15 througha water supply conduit 16.

A shifting section 20 has a gas inlet connected to a gas outlet of thereforming section 10 by a gas conduit 21 and has a shift catalyst 22inside. The shifting section further has a first temperature detector 23for detecting the gas temperature on an inlet side and a secondtemperature detector 24 for detecting the gas temperature on an outletside. The shift catalyst is a cerium oxide and platinum supported on ahoneycomb-shaped catalyst carrier composed of cordierite.

A purifying section 30 has a gas inlet connected to a gas outlet of theshifting section 20 by a gas conduit 31 and has a purifying catalyst 32inside. The purifying section further has a first temperature detector33 for detecting the gas temperature on an inlet side and a secondtemperature detector 34 for detecting the gas temperature on an outletside. The purifying catalyst is platinum and ruthenium supported on ahoneycomb-shaped catalyst carrier composed of cordierite. A gas conduit41 provided at an outlet of the purifying section 30 supplies hydrogento a fuel cell system or the like. The gas conduit 31 is connected to anair supply section 36 by a gas conduit 35, and air is supplied to thegas conduit 31 from the air supply section.

Next, operation of the hydrogen producing apparatus of this embodimentwill be explained.

The heating section 12 is operated to heat the reforming catalyst in thereforming chamber 11. The feedstock hydrocarbon and water are suppliedto the reforming chamber 11 from the feedstock supply section 13 and thewater supply section 15, respectively, to cause a steam reformingreaction to proceed. The reformed gas is supplied through the gasconduit 21 to the shifting section 20 to cause a shift reaction toproceed, and the shifted gas is supplied through the gas conduit 31 tothe purifying section 30. At this time, air is supplied from the airsupply section 36 to the gas conduit 31, and the air is mixed with theshifted gas. The gas purified in the purifying section 30 is supplied tooutside through the gas conduit 41.

One of the characteristics of this embodiment is the use of the ceriumoxide and Pt for the catalyst of the shifting section 20. This catalystenables a large reduction of carbon monoxide in comparison with a Fe—Crbased catalyst used at a relatively high temperature. Also, incomparison with the Cu—Zn based catalyst used conventionally, thiscatalyst is characterized by having resistance to high temperature andresistance to deterioration in catalytic activity caused by repetitionof oxidation and reduction. However, it is slightly inferior in lowtemperature activity to the Cu—Zn based catalyst whose activity has notdeteriorated. Thus, the carbon monoxide concentration tends to becomehigh at the outlet of the shifting section. The increase of the carbonmonoxide concentration leads to an increase of load in the purifyingsection. Consequently, the purifying section using a conventionalPt-based or Ru-based catalyst becomes unable to purify sufficiently insome cases.

In the Pt-based purifying catalyst, the catalytic activity at lowtemperatures deteriorates with increase of carbon monoxideconcentration. Also, with the increase of carbon monoxide concentration,there is a need to increase the amount of oxygen introduced to thepurifying section. In the case of the operation under the conditionssuitable for the carbon monoxide concentration, there arises a need,eventually, to make the catalyst temperature high. When the catalysttemperature becomes high, however, carbon dioxide reacts with hydrogento produce carbon monoxide and water, thereby making it impossible todecrease the carbon monoxide concentration sufficiently.

The Ru-based purifying catalyst causes a methanation reaction of carbonoxide and hydrogen, which is a reaction of decreasing carbon monoxide.Also, a methanation reaction of carbon dioxide and hydrogen proceedssimultaneously. Since these reactions are both exothermic, the reactionsproceed rapidly when the catalyst temperature becomes higher than acertain temperature. Since the Ru-based purifying catalyst also causesan oxidation reaction to decrease carbon monoxide, the amount of oxygenintroduced to the purifying section needs to be increased with increaseof carbon monoxide concentration, so that the catalyst temperaturebecomes high to some extent. With the increase of catalyst temperatureand carbon monoxide concentration, the methanation reactions proceed tomake the catalyst temperature high, so that the carbon monoxideconcentration may be eventually increased in some cases.

Therefore, the present invention uses the Pt catalyst and the Rucatalyst for the purifying section. In the Pt catalyst, the catalyticactivity deteriorates at low temperatures with increase of carbonmonoxide concentration. On the other hand, the Ru catalyst is active foroxidation reaction of carbon monoxide even at relatively lowtemperatures. Thus, when the Pt catalyst and the Ru catalyst arecombined, the Ru catalyst causes carbon monoxide to react to some extentand the amount of carbon monoxide adsorbed on the Pt catalyst istherefore reduced, so that the catalytic activity for oxidation reactionof carbon monoxide is retained. This makes it possible to decrease ahigh concentration of carbon monoxide even at relatively lowtemperatures in comparison with the use of only the Pt catalyst. Whenthe catalyst temperature is high, on the other hand, the oxidationreaction of carbon monoxide by the Pt catalyst is more likely to occurso that the methanation reaction by the Ru catalyst is less likely tooccur. When the methanation reaction and the oxidation reaction ofcarbon monoxide are compared, the oxidation reaction of carbon monoxideis less exothermic; therefore, it is possible to suppress heatgeneration over the catalyst and thereby prevent the vicious circle thatthe increase of the catalyst temperature causes the methanation reactionto proceed.

As described above, the hydrogen producing apparatus of the presentinvention enables reduction of carbon monoxide even at relatively lowtemperatures; thus, even if oxygen is supplied in an amount suitable foroxidation of a high concentration of carbon monoxide, the catalysttemperature does not become high eventually, so that it is possible todecrease carbon monoxide.

This embodiment is characterized by the use of the cerium oxide and Ptfor the catalyst of the shifting section. As described above, there is aproblem specific to this catalyst that the carbon monoxide concentrationbecomes relatively high at the outlet of the shifting section incomparison with the conventional shift catalysts. In order to solve thisproblem, this embodiment has a special constitution that the shiftingsection as described above is connected to the purifying section havingthe catalyst composed of the combination of the Pt catalyst and the Rucatalyst. Thus, in order to effectively decrease a high concentration ofcarbon monoxide, it is necessary to widen the temperature range in whichthe catalyst of the purifying section can be used.

In the following, the combination ratio of the Pt catalyst and the Rucatalyst will be described.

When the ratio of the Ru catalyst is high, the methanation is morelikely to proceed and the upper limit of catalyst operating temperaturetherefore becomes low. When the ratio of the Ru catalyst is low, on theother hand, the activity of the Pt catalyst cannot be retained at lowtemperatures and the lower limit of catalyst operating temperaturetherefore becomes high.

When the carbon monoxide concentration is relatively low at the outletof the shifting section, the amount of Ru catalyst is reduced to raisethe upper limit of operating temperature at high temperatures. When thecarbon monoxide concentration is relatively high, the amount of Rucatalyst is increased to lower the lower limit of operating temperatureat low temperatures.

In consideration of the reactivity at low temperatures and hightemperatures, the number of Ru atoms of the purifying catalyst includingPt and Ru is desirably set in a range of not less than one tenth and notmore than 1 of the number of Pt atoms. Also, the use of the catalystcomprising a Pt—Ru alloy allows the catalyst operating temperature rangeto become wider, making it possible to successfully deal with a highconcentration of carbon monoxide. In the use of the Pt—Ru alloy, wherePt and Ru catalysts exist in closer vicinity, carbon monoxide isconsumed more effectively over the Ru catalyst and the activity of thePt catalyst is therefore more likely to be retained at low temperatures.At high temperatures, the methanation reactions are suppressed moreeffectively than in the use of the catalyst composed of only Ru.

Further, combination of the Rh catalyst and the Pt catalyst alsoproduces the same effects as the Ru catalyst. This is because the Rhcatalyst is also active for oxidation reaction of carbon monoxide evenat low temperatures.

This embodiment used a cerium oxide as the metal oxide in combinationwith the Pt catalyst to constitute the shift catalyst, but the metaloxide is not limited to the cerium oxide. For example, a metal oxide ofZr, Zn or the like exhibits catalytic activity for the shift reactionwhen combined with the Pt catalyst. Further, the platinum group metalcatalyst is not limited to Pt, and other platinum group metals such asRu, Pd and Rh may also be applicable.

EXAMPLE 1

The following will describe an example of the operation of the hydrogenproducing apparatus of Embodiment 1.

Methane gas was used as the feedstock, and 1 mol of methane gas wasadded with 2.5 mol of water and was steam reformed. The resultant outletgas in the reforming section 10 was a hydrogen gas containing about 10%of carbon monoxide and about 10% of carbon dioxide. When this hydrogenproducing apparatus was operated in a steady manner, the carbon monoxideconcentration of the outlet gas of the shifting section 20 was about 1%.At this time, the temperatures of the shift catalyst upstream anddownstream of the hydrogen gas flow were detected by the firsttemperature detector 23 and the second temperature detector 24 toexamine if the shifting section was kept at a temperature capable ofdecreasing carbon monoxide effectively.

Air was added to this hydrogen gas from the air supply section 36 suchthat the amount of oxygen contained in the air became four times theamount of oxygen necessary for oxidation reaction of carbon monoxide,and the resultant gas was supplied to the purifying section 30 havingthe purifying catalyst composed of the combination of the Pt catalystand the Ru catalyst. At this time, the temperatures of the purifyingcatalyst upstream and downstream of the hydrogen gas flow were detectedby the first temperature detector 33 and the second temperature detector34 to find the state of the purifying catalyst. As a result, when thetemperature of the first temperature detector 33 was in a range of about80 to 120° C., the carbon monoxide concentration of the outlet hydrogengas was successfully reduced to 20 ppm or lower. At this time, thesecond temperature detector was about 150 to 190° C. due to heatgeneration caused by oxidation.

In a hydrogen producing apparatus having the same constitution as theabove apparatus except for the use of the Pt catalyst for the catalystof the purifying section, when the temperature of the first temperaturedetector in the purifying section was 80° C., reduction of carbonmonoxide was not possible, and when it was in a temperature range ofabout 110 to 120° C., the carbon monoxide concentration at the outletcould be reduced to 20 ppm or lower.

In the case of using the Ru catalyst for the catalyst of the purifyingsection, the carbon monoxide concentration at the outlet could bereduced to 20 ppm or lower only when the temperature of the firsttemperature detector in the purifying section was in a range of about 80to 110° C. When it was 110° C. or higher, the outlet temperature becamehigh due to increased heat generation caused by the methanationreaction, thereby making it impossible to decrease the carbon monoxide.

These results demonstrate that the purifying catalyst composed of thecombination of the Pt catalyst and the Ru catalyst has a large range ofcatalyst operating temperature and effective reduction of a highconcentration of carbon monoxide is therefore possible.

Embodiment 2

FIG. 2 shows the constitution of a hydrogen producing apparatus of thisembodiment.

The difference from FIG. 1 is that a heater 25 is provided as heatingmeans in the shifting section 20. The heater 25, which is, for example,an electric heater, minimizes condensation of water especially in theshifting section when the apparatus is started, shortens the start-uptime, and allows the activity of the shift catalyst to be maintained.

The dew point of the reformed gas can be calculated on the basis of theamounts of the feedstock and water supplied. For example, when thefeedstock is methane and water is supplied in an amount three times thenumber of moles of the methane, provided that 100% of the methane issteam reformed into carbon dioxide and hydrogen, the steam partialpressure of the gas after the reforming reaction becomes one sixth fromthe reaction formula. Thus, the dew point of the gas can be easilycalculated.

According to the present invention, the operation of the heater 25 iscontrolled such that the temperature of the gas before and after theshift catalyst detected by the first temperature detector 23 and thesecond temperature detector 24 of the shifting section becomes atemperature not lower than the dew point. This makes it possible toprevent condensation of water in the shifting section, to shorten thestart-up time of the apparatus, and to prevent deterioration of theproperties of the shift catalyst. Further, in the steady operation, therespective sections of the apparatus including the shifting section areeventually heated to a temperature not lower than the steam dew point bythe heat contained in the reformed gas, so that condensation of waterdoes not occur in the apparatus and stable supply of hydrogen thereforebecomes possible.

Embodiment 3

FIG. 3 shows the constitution of a hydrogen producing apparatus of thisembodiment. The apparatus has almost the same constitution as that ofEmbodiment 2 except that the heater 25 is removed from the shiftingsection and an air supply section 26 is connected to the gas conduit 21through a gas conduit 27.

In this embodiment, the air supply section 26 supplies air to thereformed gas to heat the shifting section and the shift catalyst. Also,in the use of the shift catalyst of the present invention, oxygen in thesupplied air oxidizes part of the reformed gas component readily, andheat is generated upon the oxidation to heat the shifting section andthe shift catalyst.

Accordingly, in the same manner as in Embodiment 2, this embodimentmakes it possible to heat the shifting section to prevent watercondensation in the shifting section, to shorten the start-up time ofthe apparatus, and to prevent deterioration of the properties of theshift catalyst. Further, it is possible to control the oxidationreaction over the shift catalyst, that is, the amount of heatgeneration, by the amount of air supplied, so that the catalysttemperature can be controlled easily.

Embodiment 4

FIG. 4 shows the constitution of a hydrogen producing apparatus of thisembodiment. The apparatus has almost the same constitution as that ofEmbodiment 2 except that the heater 25 is removed from the shiftingsection and an air supply section 17 is connected to the feedstocksupply conduit 14 through a gas conduit 18.

In this embodiment, as means for suppressing water condensation, thefeedstock is mixed with air and supplied to the reforming catalyst. Theair is supplied to the feedstock gas to oxidize part of the feedstock,so that the amount of water necessary for the reforming reaction can bereduced, and the dew point of the reformed gas can be lowered bynitrogen in the air. As a result, the amount of water condensation canbe reduced in the respective sections of the apparatus. Further, thenitrogen gas in the air increases the gas flow rate to increase theamount of heat contained in the gas, so that the respective sections canbe heated promptly.

The reforming catalyst is heated both by the heating section 12 and byheat generated upon the oxidation of part of the feedstock over thereforming catalyst by the air supplied.

It is noted that the Cu—Zn based catalyst, which is conventionally usedas the shift catalyst, is not suited for this embodiment. In thisembodiment, heating is performed by introducing air, and the Cu—Zn basedcatalyst is not preferable since the activity of this catalyst islowered due to oxidation by air. In view of this, it is preferable touse a platinum group metal whose catalytic activity is hardly lowereddue to oxidation/reduction, particularly Pt or Rh, and a metal oxidesuch as cerium oxide, zirconium oxide or zinc oxide for the shiftcatalyst.

EXAMPLE 2

The following will describe an example of the operation of the hydrogenproducing apparatus of Embodiment 2.

First, upon the start of the apparatus, the heating section 12 wasoperated to start the heating of the reforming chamber 11. Subsequently,1 mol of feedstock methane gas was added with 2.5 mol of water andsupplied to the reforming chamber 11 of the reforming section. The flowrate of the methane was set at 300L/hour. The amount of heating by theheating section 12 was controlled such that the temperature of thereforming catalyst became 700° C., and the steam reforming reaction wasallowed to proceed.

Immediately after the start of the apparatus, since the temperatures ofthe respective sections including the shifting section 20 are almostclose to room temperature, water condensation takes place. The dew pointof the reformed gas is about 45° C. In order to prevent watercondensation in the shifting section, the heater 25 was operated suchthat the gas temperatures detected by the first temperature detector 23and the second temperature detector 24 became not lower than 45° C. Thisenabled prevention of water condensation in the shifting section,especially over the catalyst. The power consumption of the heater 25 wasthen about 100 W.

During the steady operation, in order to effectively decrease the carbonmonoxide in the reformed gas supplied to the shifting section by theshift reaction with water, the heater was operated such that thetemperature inside the shifting section became about 300° C. Without theoperation of the heater 25, it took about 60 minutes for the temperatureof the shifting section to rise to about 300° C. at which the operationbecame stable, but this time was successfully shortened to about 30minutes by operating the heater 25.

It is noted that this operation time varies depending on the size of theapparatus, the supply amount of feedstock and the controllingtemperature of the heater.

Since the temperature of the reformed gas becomes about 700° C. duringthe steady operation, this heat was utilized to sequentially heat therespective sections of the apparatus, so that the shifting section couldbe operated in a stable manner.

EXAMPLE 3

The following will describe an example of the operation of the hydrogenproducing apparatus of Embodiment 3.

The apparatus was operated in almost the same manner as in Example 2.Air was supplied to the reformed gas from the air supply section 26 at60 L/hour to oxidize the reformed gas over the shift catalyst, and theshift catalyst was heated by heat generated upon the oxidation. Theamount of air supplied to the shifting section needs to be set dependingon the amount of hydrogen to be generated. With respect to the amount ofheat generation, when air is supplied at 60 L/hour, heat of about 320kj/hour is expected to be generated. This corresponds to a heater with aheat generation of about 89 W. Thus, this embodiment without the heater25 could achieve the start-up time equivalent to that of Example 2.

Since a large amount of hydrogen is contained in the gas reformed by thesteam reforming reaction of hydrocarbon, it is possible to cause theoxidation reaction to proceed smoothly even at low temperatures rightafter the start.

In this embodiment, the amount of air supplied from the air supplysection 26 was controlled such that the oxygen concentration became 4%or less in consideration of the explosion limit concentration of thehydrogen gas in the reformed gas.

EXAMPLE 4

The following will describe an example of the operation of the hydrogenproducing apparatus of Embodiment 4.

The apparatus was operated under almost the same conditions as inExample 2. However, upon the start, air was supplied to the feedstockmethane before it was introduced into the reforming section 10 tooxidize the feedstock methane, the amount of the air being about onefourth of the amount necessary for complete oxidation of the feedstock.Provided that one fourth of the methane was oxidized since the oxidationof methane takes precedence over the steam reforming reaction, water wassupplied such that the molar amount of water including the watergenerated by the oxidation corresponded to 2.5 times that of theremaining methane.

By supplying air to the feedstock before the introduction into thereforming section, the dew point of the reformed gas becomes about 40°C., so that water condensation is less likely to occur than the casewithout air introduction. Further, the introduction of air increases theamount of gas, and the nitrogen gas in the air increases the gas flowrate to increase the amount of heat contained in the gas, so that therespective sections are heated more promptly. Consequently, it tookabout 30 minutes for the temperature of the shifting section to rise toabout 300° C. in Example 2, but this example succeeded in shortening thetime to about 25 minutes.

With regard to the air supply from the air supply section 17, even if itis conducted during the steady operation as well as at the start of theapparatus, a large problem does not occur. Although this example usedmethane as the feedstock hydrocarbon, it is possible to use anycarbon-containing organic compound commonly used as the feedstock of thesteam reforming, for example, natural gas, hydrocarbon such as LPG,alcohol such as methanol, or naphtha.

EXAMPLE 5

The shift catalyst used in the example of the present invention wasprepared as follows. A powder of cerium oxide CeO₂ was impregnated withan aqueous solution of chloroplatinic acid and was subjected to aheating treatment of about 500° C. to cause the CeO₂ to support 3 wt %Pt. The CeO₂ with Pt supported thereon was coated to a honeycomb-shapedcatalyst carrier composed of cordierite having a diameter of 100 mm anda length of 50 mm, to prepare the shift catalyst.

As a comparative example, a Cu—Zn catalyst was used in place of the CeO₂with Pt supported thereon. When the PtCeO₂ catalyst was used,deterioration of the catalytic activity of the shift catalyst was hardlyobserved even after start and stop were repeated 10 times or more. Thisis because the Pt—CeO₂ catalyst is hardly affected by the deteriorationof the activity caused by oxidation.

On the other hand, in the use of the Cu—Zn catalyst, when start and stopof the apparatus were repeated 10 times or more, the carbon monoxideconcentration of the shifted gas became twice in comparison with that ofthe first start, showing deterioration of the catalytic activity. Thisis because the catalyst is oxidized during the stop and is thereforedeteriorated in activity.

As described above, the Pt—CeO₂ catalyst of the present invention isless susceptible to deterioration in catalytic activity than theconventional Cu—Zn catalyst. This appears to be mainly due to thedifference in carbon monoxide adsorbing property between Pt and Cu. Thatis, Pt is less likely to sinter due to oxidation. In contrast, Cu ismore likely to sinter due to oxidation than Pt, and the carbon monoxideadsorbing property is deteriorated consequently. The oxidation of thecatalyst takes place upon air introduction or water condensation.

EXAMPLE 6

A comparison of the properties of the shift catalyst was made betweenthe Pt—CeO₂ catalyst and the Rh—CeO₂ catalyst using the apparatus ofFIG. 2.

The basic properties of the Rh—CeO₂ catalyst as the shift catalyst arehardly affected by deterioration in catalytic activity due to oxidation,so the Rh—CeO₂ catalyst showed properties almost equivalent to thePt—CeO₂ catalyst. In the case of the Rh—CeO₂ catalyst, however, theconcentration of methane in the shifted gas was slightly increased,since it has better activity for the methanation reaction of hydrogenand carbon dioxide or carbon monoxide than the Pt—CeO₂ catalyst.

In a comparison at a catalyst temperature of 300° C., the methaneconcentration of the shifted gas was 0.1% (on a basis of dry gas) forthe Pt—CeO₂ catalyst as opposed to 0.2% (on a basis of dry gas) for theRh—CeO₂ catalyst. However, the carbon monoxide concentration at theoutlet was retained at an almost constant value. Since this extent ofincrease in methane concentration presents no practical problem, theRh—CeO₂ catalyst can also be used as the shift catalyst.

In addition, it was confirmed that only this combination of the Pt andRh catalysts did not exhibit the catalytic activity and that otherplatinum metal Ru or Pd also exhibited similar activity for shiftreaction although the properties slightly varied depending on the metal.

EXAMPLE 7

Various shift catalysts were examined for their activities for shiftreaction. As a result, it was confirmed that a catalyst prepared byusing ZrO₂, ZnO, or a mixture or solid solution of CeO₂ with one ofthese oxides as the metal oxide could serve as the shift catalyst havingexcellent oxidation resistance that the Cu—Zn catalyst is lacking in.The activity for shift reaction, however, varied slightly depending onthe metal oxide. For example, when ZrO₂ was used, the methanationreaction of hydrogen and carbon dioxide or carbon monoxide wasfacilitated, so that the methane concentration at the outlet of theshifting section tended to increase slightly. Although it may differaccording to the condition under which the catalyst is used, in acomparison at a catalyst temperature of 300° C., the methaneconcentration at the outlet of the shifting section was 0.1% (on a basisof dry gas) for the Pt—CeO₂ catalyst as opposed to 0.15% (on a basis ofdry gas) for the Pt—ZrO₂ catalyst. Also, when ZnO was used, the activityfor shift catalyst was improved at low temperatures since it is superiorin donating oxygen at low temperatures to CeO₂; however, when it wasused at high temperatures such as 500° C. or higher, the catalyticactivity tended to deteriorate since the reducing tendency of the Znoxide increases.

Embodiment 5

FIG. 5 is a longitudinal cross-sectional view schematically showing theconstitution of a shifting section of a hydrogen producing apparatusaccording to this embodiment.

A shifting section 50 is composed of a first reaction chamber 51, asecond reaction chamber 52 and a narrowed part 53 connecting bothchambers, and the first reaction chamber 51 and the second reactionchamber 52 are provided with a first catalyst 61 and a second catalyst62, respectively. Diffusing plates 63 and 64 are provided upstream ofthese catalysts, respectively. The first reaction chamber 51 has areformed gas inlet 55 connected to the reforming section 10, and thesecond reaction chamber 52 has a shifted gas outlet 56 connected to thepurifying section 30. In order to keep the reaction chambers at aconstant temperature, the outer surfaces are covered, where necessary,with a heat insulating material 54 composed of ceramic wool.

The following will describe an example that a reformed gas obtained bysteam reforming natural gas in the reforming section 10 is supplied tothe shifting section.

The composition of the gas obtained by steam reforming natural gasvaries according to the reaction temperature over the reformingcatalyst, but its average composition excluding steam is comprised ofabout 80% hydrogen, about 10% carbon dioxide and about 10% carbonmonoxide. The reformed gas introduced from the inlet 55 first reactsover the first catalyst 61 so that the CO concentration is decreased to1 to 2%. The reformed gas having passed through the first catalystreacts over the second catalyst 62 until the CO concentration becomesabout 0.1 to 0.8%, is discharged from the outlet 56 to the purifyingsection 30 or the like, and is supplied to a fuel cell or the like.

Next, a description will be given on the principle of the operation ofthis apparatus. The CO shift reaction is an equilibrium reactiondependent on the temperature, and in theory of equilibrium, the lowerthe reaction temperature becomes, the larger the reduction of the COconcentration becomes. However, since the reaction rate over thecatalyst is low at low temperatures, the CO shift catalyst exhibitsproperties that the CO concentration verses temperature goes through theminimum, as shown by the solid line of FIG. 6. Thus, the higher thecatalytic activity becomes at low temperatures, the lower the COconcentration becomes. Generally speaking, a copper-based catalyst usedas the CO shift catalyst, such as a copper-zinc catalyst or acopper-chromium catalyst, has high activity at low temperatures and iscapable of the CO shift reaction at about 150 to 300° C., so that the COconcentration can be reduced from a few hundred to a few thousand ppm.The copper-based catalyst, however, needs to be activated after beingcharged to a reaction vessel by passing a reducing gas such as hydrogenor reformed gas as an initial operation. Also, the copper-based catalysthas a low thermal resistance to about 300° C.; therefore, in order toprevent the catalyst temperature from exceeding this withstandtemperature due to the reaction heat generated upon the activation, thereducing gas is supplied in a diluted state or in a small amount suchthat the reaction proceeds gradually. The copper content of the catalystalso has an influence on the time required for the activation. Ensuringlife reliability would require a copper content of a few ten wt %,thereby necessitating a long time for the activation.

Also, in the CO shift reaction, gas velocity per catalyst volume (spacevelocity: SV) normally needs to be not more than 1000 per hour,requiring a large amount of catalyst and thereby an increased thermalcapacity; it thus takes a long time to raise the temperature of thecatalyst when the apparatus is started. Therefore, heating may beperformed from outside the reaction chamber, for example, by an electricheater, or the temperature of the reformed gas supplied may beheightened, in order to speed up the temperature rise. However, sincethe copper-based catalyst has a low thermal resistance, such rapidheating as to cause a local temperature rise is not desirable.

When the apparatus is stopped, the internal pressure of the reactionchamber decreases with decrease of the temperature of the apparatus, toallow a small amount of air to get in from outside. Thus, when theapparatus is stopped and started repeatedly over a long period, thecopper-based catalyst is gradually deteriorated. This necessitates ameans for preventing air inclusion or the like and makes the apparatusmore complicated.

On the other hand, as in the apparatus of the present invention, whenthe platinum metal group catalyst is used as the CO shift catalyst, thelong-time activation and reducing treatment are unnecessary. Also, sincethis catalyst has high thermal resistance, no problem occurs even whenthe temperature rises to about 500° C. locally at the time of the start;thus, rapid heating is possible by supplying a high temperature reformedgas and prompt start-up of the apparatus is therefore possible. Further,since this catalyst is resistant to deterioration even if a small amountof air is included, there is no need for specific means such asoxidation preventing means.

The properties of the CO shift reaction are influenced by temperaturedistribution of the shift catalyst from the upstream to the downstream.The temperature of the upstream, where the CO concentration is high, ispreferably high since the reaction rate is high at high temperatures,whereas the temperature of the downstream, where the equilibrium COconcentration is influential, is desirably low. Thus, as in thisapparatus, when the CO shift catalyst is divided and accommodated intoplural chambers with a heat radiating part or a cooling part disposedbetween the chambers to control the amount of heat radiation or cooling,the CO can be decreased with a smaller amount of catalyst.

Further, the higher the temperature is, the greater the space velocitybecomes, but when the temperature gets too high, the reverse reaction ofthe reforming reaction begins to proceed to generate methane, so thatthe amount of hydrogen in the reformed gas is lowered, affecting theefficiency of the apparatus. Thus, the temperature of the first catalystis preferably not higher than 450° C. On the other hand, when thetemperature of the first catalyst is low, the space velocity needs to bedecreased, and therefore the temperature of the first catalyst ispreferably not lower than 300° C. The temperature of the first catalystcould be made lower than 300° C. if the space velocity is decreased;however, this makes the temperature difference between the firstcatalyst and the second catalyst small, so that dividing the catalystinto plural chambers may become less effective and the volume of thereaction vessel may become larger due to the division.

When the temperature of the second catalyst is higher than that of thefirst catalyst, the CO which has been reduced by the first catalyst isincreased again by the reverse reaction, and therefore the temperatureof the second catalyst is preferably lower than that of the firstcatalyst. This also applies to the case where the number of the catalystchambers is three or more.

The lower the space velocity is, the higher the properties become whenthe catalyst temperature is low, whereas the higher the space velocityis, the more unlikely the methanation proceeds at high temperatures.Thus, the volume of the catalyst of the upper chamber is preferablysmaller than that of the catalyst of the lower chamber.

The CO shift catalyst preferably contains a cerium oxide and platinum toproduce high properties. The particle size of the cerium oxide ispreferably 0.1 to 15 μm, and if the particle size is larger than thisrange, dispersion property of the platinum is lowered, which may lead toinsufficient properties. When the particle size is smaller than 0.1 μm,separation from the honeycomb-shaped catalyst carrier, collapse ofpellets or the like may occur, and the life characteristics are likelyto deteriorate.

A diffusing part or a mixing part is preferably disposed between thechambers of the catalyst. The CO shift catalyst having a large volumetends to have temperature distribution in its cross-sectional direction,so variations in CO concentration may occur after passage of thecatalyst between the central part and the outer part. Thus, by providingthe mixing part or the diffusing part, the catalyst of the lower chamberfunctions effectively, so that higher properties can be obtained.

The amount of platinum group metal supported on the shift catalyst ispreferably larger in the lower chamber than in the upper chamber. Whenthe amount of platinum group metal supported is large, methanation islikely to proceed, and this tendency is evident in the upper chamberwhere the catalyst temperature is high. On the other hand, the activityis improved at low temperatures when the amount of platinum group metalsupported is increased. Thus, by increasing the amount of platinum groupmetal supported on the catalyst of the lower chamber where themethanation reaction is less likely to proceed, higher properties can beobtained with a smaller volume of catalyst.

This embodiment used platinum supported on a cerium oxide as theplatinum group metal catalyst, but it is also possible to use a platinumgroup metal such as rhodium, palladium or ruthenium supported on acarrier of alumina, zirconium oxide, magnesium oxide, zinc oxide,titanium oxide or silicone oxide.

In this embodiment, the honeycomb-shaped carrier composed of cordieritewas coated with the cerium oxide supporting a platinum salt to producethe CO shift catalyst, but palletized alumina may also be used tosupport the catalyst to produce the CO shift catalyst. Also, metal suchas stainless steel or ceramic wool may be used as the honeycomb-shapedcarrier.

Embodiment 6

In a shifting section 50 a of this embodiment, the narrowed part 53connecting the first reaction chamber 51 and the second reaction chamber52 is provided with a cooling water supply conduit 57 as shown in FIG.7.

Since the CO shift reaction is an equilibrium reaction, when the ratioof reactant steam is large, more CO reduction is possible. By providingthe cooling part with the cooling water supply conduit 57, the gas to beintroduced to the second reaction chamber can be cooled by the latentheat of water evaporation, and further, the equilibrium in the CO shiftreaction can be shifted advantageously, so that the CO can be reducedmore effectively.

Embodiment 7

In a shifting section 50 b of this embodiment, the part connecting thefirst reaction chamber 51 and the second reaction chamber 52 iscomprised of plural pipes 53 b and is provided with a cooling fan 58, asshown in FIG. 8.

Although the cooling efficiency depends on the surface area of thepipes, since the connecting part of this embodiment is comprised of theplural parts, effective cooling is possible, and the length of theconnecting parts can be shortened and the apparatus can therefore bedownsized. Also, the provision of the cooling fun 58 enables moreeffective cooling. By providing a device for detecting the temperatureof the second catalyst 62 and a controlling unit for controlling theoperation or the number of revolutions of the cooling fun 58 on thebasis of the detected temperature, the catalyst temperature can beconstantly maintained at an optimum value. Further, air heated byheat-exchange at the cooling part can be utilized as air to be suppliedto a combustion section for heating the reforming section, or can beutilized to heat the feedstock or water used for the reforming, wherebythe efficiency of the apparatus can be improved.

Embodiment 8

This embodiment uses, as the second catalyst 62 of FIG. 7, acopper-based catalyst, for example, a honeycomb-shaped catalyst carriercomposed of cordierite coated with a cooper-based catalyst. Herein, thecopper-based catalyst refers to a CO shift catalyst containing copper asa component of its activity and is, for example, a copper-zinc catalyst,a copper-chromium catalyst, or a copper-zinc or copper-chromium basedcatalyst with alumina, silica, zirconium or the like added thereto. Theprovision of the copper-based catalyst capable of the CO shift reactionat low temperatures enables more reduction of the CO concentration ofthe gas having passed through the second chamber. Further, since thefirst chamber is provided with the platinum group metal catalyst havinghigh thermal resistance, the copper-based catalyst having relatively lowthermal resistance is prevented from being exposed to high temperaturesat the time of the start, and the influence of the deterioration isdecreased.

It is preferable to further provide the platinum group metal catalystdownstream of the copper-based catalyst. When the apparatus is suspendedor stopped for a long term, a small amount of air may get in theapparatus from outside, and the inclusion of air causes the copper-basedcatalyst to deteriorate gradually. Onto the platinum group metalcatalyst, hydrogen or CO is adsorbed even while the apparatus isstopped; thus, when the platinum group metal catalyst is providedupstream and downstream so as to sandwich the copper-based catalyst, thesmall amount of oxygen is consumed over the platinum group metalcatalyst and the deterioration of the copper-based catalyst cantherefore be suppressed.

EXAMPLE 8

The first catalyst and the second catalyst were produced by coatinghoneycomb-shaped carriers composed of cordierite having the samediameter but having a length of 20 mm and 60 mm, respectively, with apowder of cerium oxide having a particle size of 15 μm with platinumsupported thereon, and were disposed in the first chamber 51 and thesecond chamber 52, respectively. A reformed gas consisting of carbonmonoxide (8%), carbon dioxide (8%), steam (20%), and hydrogen (balance)was introduced from the reformed gas inlet 55 at a flow rate of 10 literper minute. The temperatures of the first catalyst and the secondcatalyst were controlled to become 400° C. and 250° C., respectively,and the CO concentration of the gas released from the shifted gas outlet56 was measured by gas chromatography and was turned out to be 3000 ppm.Subsequently, after the gas of the reaction chamber was replaced withnitrogen, air was supplied, and the reformed gas was supplied again; theCO concentration of the outlet gas was measured and was turned out to be3000 ppm. Further, the same operations were repeated 50 times, and theCO concentration was measured in the same manner and was turned out tobe 3200 ppm.

EXAMPLE 9

In the same manner as in Example 8, the CO concentration of the gasreleased from the shifted gas outlet 56 was measured by varying thetemperature of the first catalyst of Example 8 to 250° C., 275° C., 300°C., 400° C., 450° C. and 475° C., and it was turned out to be 7000 ppm,7200 ppm, 3100 ppm, 3000 ppm, 3100 ppm and 3500 ppm. The methaneconcentration of the gas was also measured, and as a result, no methanewas detected at 400° C. or lower, and it was 0.5% at 450° C. and 1.1% at475° C.

EXAMPLE 10

In the same manner as in Example 8 except for the use of powders of acerium oxide having a particle size of 0.05 μm, 0.1 μm, 5 μm, 15 μm and17 μm, respectively, the CO concentration of the outlet gas was measuredand was turned out to be 2900 ppm, 3000 ppm, 3400 ppm, 3500 ppm and 5000ppm. Subsequently, after the gas of the reaction chamber was replacedwith nitrogen, air was supplied, and the reformed gas was suppliedagain; the CO concentration of the outlet gas was measured and wasturned out to be 3800 ppm, 3000 ppm, 3400 ppm, 3500 ppm and 5100 ppm.Further, the same operations were repeated 50 times, and the COconcentration was measured in the same manner and was turned out to be9000 ppm, 3100 ppm, 3500 ppm, 3600 ppm and 8000 ppm.

COMPARATIVE EXAMPLE 1

Without dividing the reaction chamber, one reaction chamber was used andwas provided with a catalyst comprising the same catalyst as that ofExample 8 supported on a carrier having a length of 80 mm. Under thesame conditions as those of Example 8, the CO concentration of theoutlet gas was measured, and the minimum value was turned out to be 7000ppm. Subsequently, after the gas of the reaction chamber was replacedwith nitrogen, air was supplied, and the reformed gas was suppliedagain; the CO concentration of the outlet gas was measured at the sametemperatures and was turned out to be 7100 ppm. Further, the sameoperations were repeated 50 times, and the CO concentration was measuredin the same manner and was turned out to be 7200 ppm.

COMPARATIVE EXAMPLE 2

By providing a copper-zinc catalyst in place of the platinum catalyst ofthe Comparative Example 1, the measurement was conducted in the samemanner, and the CO concentration of the outlet gas was turned out to be1000 ppm. Subsequently, after the gas of the reaction chamber wasreplaced with nitrogen, air was supplied, and the reformed gas wassupplied again; the CO concentration of the outlet gas was measured andwas turned out to be 200 ppm. Further, the same operations were repeated50 times, and the CO concentration was measured in the same manner andwas turned out to be 22000 ppm.

INDUSTRIAL APPLICABILITY

The present invention makes it possible to effectively decrease carbonmonoxide in a hydrogen gas generated by fuel reforming and to provide ahydrogen producing apparatus capable of supplying the hydrogen gas in astable manner with a simple constitution. Further, it realizes ahydrogen producing apparatus which can operate in a stable manner over along term even if start and stop operations are repeated and which needsless time for starting up the apparatus.

1. A hydrogen producing apparatus comprising: a reforming section havinga reforming catalyst which causes a reaction between a carbon-containingorganic compound as a feedstock and water; a feedstock supply sectionfor supplying the feedstock to said reforming section; a water supplysection for supplying water to said reforming section; a heating sectionfor heating said reforming catalyst; and a shifting section having ashift catalyst which causes a shift reaction between carbon monoxide andwater contained in a reformed gas supplied from said reforming section;wherein said shift catalyst comprises a platinum group metal; saidshifting section is divided into plural catalytic reaction chambers eachhaving the shift catalyst; of said plural catalytic reaction chambers,the catalyst temperature is lower in a downstream chamber than in anupstream chamber in the flowing direction of the reformed gas; and ofsaid plural catalytic reaction chambers, the amount of the platinumgroup metal of the shift catalyst is greater in a downstream chamberthan in an upstream chamber in the flowing direction of the reformedgas; and wherein in a first catalytic reaction chamber in the flowingdirection of the reformed gas, the catalyst temperature is retained atnot lower than 300° C. and not higher than 450° C.
 2. The hydrogenproducing apparatus in accordance with claim 1, wherein at least one ofa heat radiating part and a cooling part is provided between thecatalytic reaction chambers.
 3. The hydrogen producing apparatus inaccordance with claim 1, further comprising a diffusing part or a mixingpart of the reformed gas between the catalytic reaction chambers.
 4. Thehydrogen producing apparatus in accordance with claim 1, wherein saidshift catalyst further comprises cerium oxide.